You put different sizes of the image in each of the different size-based folders. For example, you could do:
Default resources: /drawable
Varied Density-based resources: /drawable-xhdpi, /drawable-hdpi, /drawable-ldpi
Medium Density Default resources: /drawable-mdpi
Medium Density Size-based Resources: /drawable-small, /drawable-normal, /drawable-large, /drawable-xlarge
You could be extra-super-duper nice and combine Density and size:
/drawable-small-ldpi, /drawable-small-mdpi, /drawable-small-hdpi, /drawable-small-xhdpi, etc...
but you usually don't have to be that precise or complete.
See:
This page, and
this one.